The proposed research will further evaluate the mechanisms by which hormones regulate the growth of kidney epithelial cells, and the alterations which occur upon malignant transformation. These studies will be based upon the use of hormone-supplemented, serum-free media for cultured kidney epithelial cells. The role of cAMP in regulating the growth and functional properties of an established kidney epithelial cell line, MDCK, will be studied in a defined medium, Medium K-1. In addition primary cultures of rabbit kidney epithelial cells will be examined in defined medium. In particular the following studies will be done: a) The mechanism by which PGE1 (and other agents which act via cAMP) increased MDCK cell growth and the expression of differentiated transport functions will be examined. The possible role of cAMP dependent protein kinase and cAMP dependent phosphodiesterase in regulating the expression of either of these functions will be examined. b) The primary defect in PGE1 independent MDCK cells, and in dibutyryl cAMP resistant MDCK cells will be examined. The effect of these defects in the variant cells on protein phosphorylation will be studied. c) The growth and functional properties of malignantly transformed MDCK cells will be further examined. d) Primary cultures of rabbit kidney epithelial cells derived from purified proximal tubules will be further characterized with regard to their functional properties. The possibility that the use of an appropriate set of hormone supplements, basal media, and substrate will permit the selective growth of particular cell types in the kidney, will be examined. The epithelial cell type(s) in the rabbit kidney which grow in response to EGF will be examined.